The Principal Investigator's long-term objectives are to understand the mechanisms and regulation of acid and buffer excretion by the kidneys. The proposed studies will specifically examine the regulation of acid-base transport in distal tubule cells. Studies will use measurements of bicarbonate and ammonia transport and also intracellular pH and chloride in isolated perfused tubules and in cultured collecting duct cells. New methods of using digital image video analysis to measure intracellular pH in multiple individual cells simultaneously will be developed and validated. In addition, these studies will establish methods to measure intracellular chloride in collecting duct cells. Several specific hypotheses will be tested. First, studies will address the nature and regulation of chloride bicarbonate exchange in the mammalian collecting duct. Three different chloride-bicarbonate exchange processes are hypothesized to exist in the collecting duct. Studies will address individual characteristics and distinct regulation by these separate chloride bicarbonate exchange processes. A second broad hypothesis is that basolateral transport processes participate in the regulation of transepithelial acid-base transport in the collecting duct. Specific changes in basolateral chloride channels and basolateral bicarbonate transport processes will be studied in conditions which alter transepithelial acid-base transport. A final hypothesis is that collecting duct ammonium transport is determined both by an apical membrane which has a low permeability to NH3, and by basolateral transport processes for NH4+. Additionally, other studies will address whether high interstitial ammonium around the collecting duct alters acid-base transport by the collecting duct both acutely and chronically. In summary, these studies will elucidate the role of several important fundamental processes in collecting duct acid-base transport.